Monrovia: A fourth member of the UN mission in Liberia, the country hardest-hit by the Ebola epidemic, has been hospitalised after testing positive for the virus.

"This is the fourth case of Ebola in the mission and UNMIL personnel continue to mourn the deaths of two colleagues who died from the disease only three months ago," a UN statement said today, referring to the United Nations Mission in Liberia.

Liberia tops the number of Ebola deaths in the world with 3,376 fatalities but has seen a clear decrease of new transmissions in the past month.

Ebola has killed 7,518 people, almost all of them in the west African epicentres of Liberia, Sierra Leone and Guinea.

The UN member tested positive yesterday and was immediately transferred to an Ebola treatment unit, Karin Landgren, the special representative of UN chief Ban Ki-moon said.

"UNMIL is taking all necessary measures to mitigate any possible further transmission -- both within the mission and beyond," Landgren said.

It said the mission had stepped up surveillance "to ensure that all people who came into contact with the staff member while symptomatic are assessed and quarantined."

"All UNMIL staff considered at risk are being isolated. The vehicles used to transport the patient and locations they visited while symptomatic are being decontaminated."

"The confirmation of an additional Ebola case in UNMIL at the start of the holiday period is a stark reminder that we must all remain vigilant until there are no cases in Liberia or west Africa," the statement said.

Ban, who recently toured west Africa for a first-hand assessment of the fight against Ebola, said on his return that the UN must learn lessons from the crisis and begin preparing now for the next outbreak of the deadly disease.

The secretary general also called for recovery efforts to be stepped up in west Africa to rebuild shattered economies, get children back in school and begin caring for Ebola orphans.

His appeal followed sharp criticism from non-governmental organisations that the United Nations, in particular the World Health Organization, were too slow to swing into action.